Instrument Description

Sensitivities

Sensitivities derived from commissioning data arelisted in Table 1. The values are valid for point sources. They were determined using a 0.4 arcsec slit, adaptive optics under an optical seeing of 0.8 arcsec. They correspond to a S/N of 10 for a 1h on-source integration in one spectral dispersion element. They were obtained by integrating the profile along the spatial direction.

Table 1. Sensitivities

Band

mJy

Magnitude

J

1.1

15.4

H

1.1

15.1

K

1.1

14.6

L

9.5

11.2

M

26

9.4

Science detectors characteristics

Typical values for the main characteristics of the science detectors are listed in Table 3.

Table 3. Typical detector characteristics

Read-out noise (rms)

10 e

Dark current

0.05 to 0.3 e/s

Gain

7 e/ADU

Saturation level

120,000 e

Adaptive Optics

The MACAO used for CRIRES is equipped with a wavefront sensor sensitive in the R band. The flux on the Avalanche Photo Diodes islimited to 1 million counts in order not to damage the devices. Starsfainter than R ~ 11 mag can be dimmed by a up ~ 9 mag thanksto a set of neutral density filters. Hence, stars brighter thanR ~ 2 mag cannot be used as AO guide stars. Stars fainter thanR ~ 17 mag will not result in any improvement. Good correction under average seeing is still obtained with stars as faint asR ~ 14 mag. Any star fainter than this will require good to excellent atmospheric conditions to provide any image quality improvement.

The field selector allows the selection of the AO star within a30 arcsec field centered on the nominal position of the science target. However, if the AO star lies at more than 10 arcsecs from the science target, the image quality is significantly improved only under good atmospheric conditions. Under excellent conditions, R < 11 mag stars as far as 20 - 30 arcsec can still lead to a modest improvement of the image quality.